The present invention relates in particular to a non-aqueous inkjet ink suitable for printing images, characters, etc., on a surface of a polyvinyl chloride sheet, etc.
Conventionally, inkjet printing, with which images, characters, etc., are printed by discharging an inkjet ink as microscopic droplets from a nozzle of an inkjet printer, is favorably used for printing mainly onto paper or other water-absorbing surface. As the inkjet ink for this purpose, an aqueous inkjet ink having a water-soluble dye or other colorant added therein is widely used in general.
However, recently, inkjet printing is being used to perform printing onto various surfaces, especially in business applications and in various other fields. There is a demand for printing images and characters, not only with good image quality but also with good water resistance, light resistance, friction resistance, etc., on the various surfaces.
For this purpose, non-aqueous inkjet inks that practically do not contain water as a solvent and use only organic solvents, and inkjet printers that use such inks are being put to practical use and becoming popularly used in place of aqueous inkjet inks.
For example, a large-size inkjet printer for printing images and characters on a surface of a polyvinyl chloride sheet, etc., that is frequently used as a medium, for example, for outdoor advertisements is becoming popularly used.
As the non-aqueous inkjet ink used in the inkjet printer, an ink containing a pigment with excellent light resistance, a binder resin for fixing the pigment onto a surface of a polyvinyl chloride sheet, etc., and an organic solvent capable of dissolving the binder resin is mainly used.
As the binder resin, any of various resins that are excellent in fixing property with respect to the surface of a polyvinyl chloride sheet, etc., such as an acrylic resin, polyester resin, polyurethane resin, polyvinyl chloride resin, nitrocellulose resin, etc., is used, and among these, a polyvinyl chloride resin, which is best in fixing property, is used favorably.
Also, by copolymerizing vinyl acetate with vinyl chloride, the solubility in the organic solvent can be improved, and images and characters printed on the surface of the polyvinyl chloride sheet can be increased in flexibility to improve scratch resistance of a print. A vinyl chloride-vinyl acetate copolymer is thus used especially favorably as the polyvinyl chloride resin.
A non-aqueous inkjet ink using a vinyl chloride-vinyl acetate copolymer or other polyvinyl chloride resin is described, for example, in JP 2004-231870A, JP 2005-23298A, JP 2005-200469A, etc.
Also, a metal coordination compound or other additive is added in a non-aqueous inkjet ink.
A surface of a nozzle plate, etc., making up a nozzle of an inkjet printer must have a property of appropriately repelling a non-aqueous inkjet ink in order to discharge the non-aqueous inkjet ink satisfactorily through the nozzle.
A coating film having a property of repelling the non-aqueous inkjet ink is thus formed on the surface of the nozzle plate, etc. As the coating film, a eutectoid coating film of a fluororesin and nickel, etc., is used.
The metal coordination compound coordinates to the nickel in the eutectoid coating film and thereby functions to improve resistance of the eutectoid coating film against the organic solvent contained in the non-aqueous inkjet ink.
Nitrogen-containing compounds, such as imidazoles, benzotriazoles, etc., can be cited as examples of the metal coordination compound.